[0001] This invention relates to a reciprocating balance weight mechanism for a piston type
internal combustion engine in which one or more reciprocating balance weights are
driven according to the motion of a rotating cam.
[0002] In certain types of engines, it is very difficult to completely dynamically balance
all of the moving masses therein. In engines of this nature the primary forces and
couples may not be compensated for by means of counterbalancing weights on the rotating
crankshaft. Secondary unbalances produced in the engine have frequently been treated
through the use of balance shafts provided in the engine. These balance shafts incorporate
eccentric weights which are rotated along with the shaft at typically twice the speed
of the engine's crank shaft to produce a rotating couple or force for counter balancing
the disturbing couple. Such balance shafts typically comprise a solid bar that is
disposed adjacent the camshaft or crankshaft with a pair of eccentric weights mounted
on the opposite ends of the bar. The weights project from the bar and are rotationally
displaced 180° from each other.
[0003] Although rotation of such a balance shaft has been found effective for balancing
a rotating couple, the rotation of the eccentrically disposed weights produces bending
of the solid shaft. This bending will result in radial deflections of the shaft which
may be of considerable dimension, particularly at higher speeds. These deflections
will cause the shaft to be bent into a somewhat S shape. This will result in the shaft
moving from the desired axial alignment with the bearing supporting the shaft, thus
imposing excessive loads on the bearings. These loads may cause excessive bearing
wear and premature bearing failure. In addition, if the shaft is driven by a gear
mounted on the shaft, the bending of the shaft will cause the gear to be deflected
out of its proper plane of rotation. Thus, the gears will not be properly aligned
and will not mesh properly. These factors will not only cause excessive wear but will
also require more power to drive the shaft. Examples of balance shafts having the
foregoing shortcomings are disclosed in the following U.S. Patents: 2,632,340; 2,838,957;
4,305,352; 4,508,069; and 4,523,553.
[0004] All of the previously known arrangements for balance shafts of the type thus far
described suffer from yet another deficiency inasmuch as the multiple bearings required
to properly suspend the shaft within the engine all consume engine power which would
otherwise be available at the flywheel. This problem is further exacerbated by the
fact that such balance shafts are commonly driven at twice the crankshaft speed which
causes greatly increased frictional losses arising from shearing of the engine's lubricant
at the bearing interfaces.
[0005] U.S. Patent 1,958,148 discloses a device for counterbalancing or diminishing vibration
occurring in stationary engine plants, in which a large mass block is elastically
supported so that when excited by a cam operated lever means, the mass block and its
spring mounting comprise a tuned absorber which will vibrate at a natural frequency
determined by its own mass and the spring constant of the elastic mounting arrangement.
Accordingly, the engine serves merely to excite the mass-spring system. This type
of system is not suitable for operation at more than a small frequency range, and
this would impose severe limitations on the available frequency response of such a
system. In other words, the system of U.S. Patent 1,958,148 would not be suitable
to produce the damping needed with modern automotive engines, which operate at wide
speed ranges.
[0006] It is an object of the present invention to provide a reciprocating balance weight
mechanism for a piston type internal combustion engine which has reduced friction
loss characteristics and no rotating bearings.
[0007] It is a further object of the present invention to provide a reciprocating balance
weight mechanism having small packaging dimensions.
[0008] It is a further object of the present invention to provide a reciprocating balance
weight mechanism which may be used to counteract both shaking forces and rocking couples
of first, second and higher order harmonics all at one.
[0009] According to the invention there is provided a balancing mechanism for reducing the
vibration of a piston type internal combustion engine having a crankshaft (6) and
a camshaft (12), said balancing mechanism comprising one or more reciprocating balance
weights (32,34) driven according to the motion of a rotating cam (22,28), with said
cam driven by either said camshaft (12) or said crankshaft (6).
[0010] Further according to the invention there is provided an internal combustion engine
comprising a crankshaft operably associated with one or more pistons and connecting
rod assemblies having one or more multiple-lobed cams attached thereto.
[0011] The driving cam is preferably integral with either the camshaft or the crankshaft.
The reciprocating balance weights are preferably driven by two rotating cams with
at least one of the cams being driven by either the engine crankshaft or the camshaft.
In one embodiment a crankshaft operably associated with one or more piston and connecting
rod assemblies has one or more multiple-lobed cams attached to it. A camshaft driven
by and synchronized with the crankshaft and having one or more intake or exhaust valves
operably associated with it has one or more multiple-lobed cams attached the to camshaft.
One or more linearly actuatable balance weights mounted within the engine is driven
reciprocably by a pair of cams comprising one of the multiple-lobed cams attached
to the crankshaft and one of the multiple-lobed cams attached to the camshaft. Thus,
the linearly actuatable balance weights preferably reciprocate between a pair of said
multiple-lobed cams.
[0012] Linearly actuatable balance weights suitable for use with the present invention preferably
comprise a generally elongate body having a cam follower mounted at either end.
[0013] The invention will now be described further by way of example with reference to the
accompanying drawings in which:
Figure 1 is a cut-away end elevation of an internal combustion engine including the
present invention.
Figure 2 is a cut-away view of the crankshaft, camshaft and balance weight mechanism
of the engine shown in Figure 1, taken along the line 2-2 of Figure 1.
Figures 3 and 4 are elevations taken along the line 3-3 of Figure 2.
Figure 5 is similar to Figure 2 and shows an alternate arrangement of the balance
weight mechanism of the present invention employing multiple balance weights.
Figure 6 is an enlarged view similar to Figures 3 and 4 showing greater detail of
the reciprocating balance weight employed with the present invention.
Figure 7 is a side elevation of the balance weight shown in Figure 6.
Figure 8 is a plan view of the balance weight of Figure 6 taken along the line 8-8
of Figure 6.
[0014] Figure 1 depicts a typical internal combustion engine which is suitable for application
of a reciprocating balance weight mechanism according to the present invention. Engine
2 is equipped with poppet type valves 4 which are actuated by a valve train mechanism
driven by camshaft 12. The camshaft is driven by crankshaft 6 via timing chain or
belt 14 which runs over idler pulley 3 as well. Connecting rod 8 and piston 10 are
associated with crankshaft 6. The lower end of the connecting rod 8a is attached to
connecting rod journal 20 of the crankshaft. Moving now to Figure 2, it is seen that
crankshaft 6 is shown in a configuration suitable for a four cylinder engine inasmuch
as the crankshaft has four connecting rod journals 20 and five main bearing journals
18. Those skilled in the art will appreciate, however, in view of this disclosure
that the reciprocating balance weight mechanism according to the present invention
could be employed with engines having not only inline but also V-type configurations
having various numbers of cylinders including odd and even numbers of cylinders. The
reciprocating balance weight mechanism according to the present invention is suitable
for use with not only gasoline internal combustion engines but also those employing
diesel combustion principles and is further suitable for engines using not only carburetors
in the conventional manner but also fuel injection systems, turbo-chargers, or other
arrangements for fuel delivery. The present system could be employed beneficially
with other reciprocating machines as well, such as piston type gas compressors. Those
skilled in the art will further appreciate that the reciprocating balance weight mechanism
according to the present invention is suitable for use not only with engines having
a camshaft located in the engine's cylinder head as shown in Figure 1, but also those
having camshafts mounted within the cylinder block. In such a case, the balance weight
could be driven by a linkage mechanism operated by the crankshaft and the camshaft.
[0015] As shown in Figure 2, camshaft 12 has a number of lobes 16 for operating engine valves
4. The camshaft is rotated upon bearing journals 26 within the engine block.
[0016] The balance weight mechanism according to the present invention is preferably driven
by multiple-lobed cams attached to the crankshaft and camshaft. Accordingly as shown
in Figures 2-6, Multiple-lobed cam 22 is attached to camshaft 12 and multiple-lobed
cam 28 is attached to crankshaft 6. Although Figures 2 and 5 show different arrangements
for the balance weight mechanism according to the present invention, the reference
numerals have been maintained constant in these figures to promote clarity in this
disclosure.
[0017] Figure 2 shows a single reciprocating balance weight mechanism, whereas Figure 5
shows a double balance weight mechanism according to the present invention. Modern
automotive internal combustion engines are required to operate at high speed with
a minimum of vibration. This requirement necessitates accurate and complete balancing
of the unbalanced forces and couples set up by rotating and reciprocating masses within
the engine. It is well known that if the forces and couples of an engine are not balanced,
excessive vibration will result. This vibration greatly increases the wear on engine
parts and reduces the life of the engine.
[0018] Engines may be out of balance, with resulting vibration and excessive wear, due to
either unbalanced forces or unbalanced couples. The unbalanced forces may be "primary"
or those operating at engine speed, or may be higher order forces which are classified
as "secondary", "tertiary", etc. corresponding to the particular harmonic of engine
speed at which they are observed. The term "unbalanced couple" as here applied, is
the equivalent of a torque or moment applied to a rigid structure. These couples may
be either so called "shaking" couples which are manifest by forces acting in a single
plane lying in the longitudinal axis of the engine or they may be rotating couples
which change their direction of application with respect to the center of the engine
either at engine speed or at some harmonic thereof.
[0019] By means of examples, two engines which are well-suited for use with the balance
weight mechanism according to the present invention are the 90° V-6 and 4 cylinder
in-line automotive engines. For a 90° V-6 engine, shaking forces are balanced. These
engines do, however, exhibit an unbalanced couple. Elimination of this unbalanced
couple will require use of two balance weight mechanisms as shown in Figure 5. The
balance mechanisms will generate a couple phased so as to oppose that couple created
by the other parts of the engine. Because the unbalanced couple will have both primary
and secondary manifestations, the profiles of the multiple-lobed cams attached to
the camshaft and crankshaft may be contoured so as to provide both primary, secondary
and higher order actuation of the balance masses. Accordingly, if the primary lift
contour of each multi- lobed cam is viewed as a primary sinusoidal function, a second
sinusoidal function of lesser magnitude could be superimposed upon the primary function
to give a secondary (i.e., higher order harmonic) actuation capability.
[0020] It has been found that the unbalanced couple of a V-type engine may produce objectionable
vibration only at one end of the engine when, for example, the engine is installed
in the "north-south" configuration in a rear-drive motor vehicle. In this event,
a balance mechanism according to the present invention may be advantageously employed
at only a single end of the crankshaft so as to economically eliminate vibration without
the necessity of a second balance weight mechanism.
[0021] Four cylinder engines are usually designed such that primary shaking forces are unbalanced
but so that there are no primary unbalanced couples. Accordingly, because it is usually
the desire of the designer to minimize cost and weight in four cylinder engines, a
single balance weight mechanism could be employed as shown in Figure 2 for a four
cylinder engine. In this manner the secondary shaking forces will be canceled at minimal
cost.
[0022] Figures 3 and 4 illustrate the nature of the movement of the balance weight mechanism.
As shown in these figures, the balance weight moves reciprocably between the multiple-lobed
cams carried on the crankshaft and camshaft. No springs or other devices are needed
to maintain the balance weight mechanism in the desired location because the balance
weight is captured between the two multiple-lobed cams which are synchronized with
the crankshaft and camshaft so that the weight merely oscillates back and forth between
the cams. As may be readily observed from Figures 3 and 4, multiple-lobed cam 22 carried
on camshaft 12 has four lobes 24, whereas multiple-lobed cam 28 carried upon crankshaft
6 has two lobes 30. Those skilled in the art will recognize that these configurations
are necessitated by the fact that the camshaft of a four cycle internal combustion
engine rotates at half the rotational speed of the crankshaft of a four cycle engine.
In the event, however, that the balance weight mechanism according to the present
invention is employed with a two cycle or, more properly, a two-stroke cycle internal
combustion engine, the multiple-lobed cams carried on the camshaft and crankshaft
would have an identical number of lobes because the camshaft and crankshaft of a two-stroke
cycle engine rotate at the same velocity. Moreover, those skilled in the art will
appreciate in view of this disclosure that a balance weight mechanism according to
the present invention could be driven with a single cam with reciprocation assured
by a spring loaded mechanism to return the balance weight to its original position
following each stroke imposed by the cam.
[0023] Turning now to Figures 6-8, the details of construction of the balance weight mechanism
are shown. As shown in these figures, the balance weight comprises a generally elongate
body 34, in this case preferably having a cylindrical configuration. Those skilled
in the art will appreciate however, in view of this disclosure that the configuration
of the weight may be adjusted to accommodate varying circumstances within the engine
which the balance weight mechanism is being applied. Elongate body 34 reciprocates
within a bore 36 provided within the engine structure 11. Bronze bearing 48 is employed
for the purpose of lining bore 46 to provide a smooth bearing surface for the reciprocation
of the balance weight. Other materials are, of course, suitable for use as bearing
material. A cam follower 36 is employed at either end of elongate body 34 for the
purpose of maintaining contact with each multiple-lobed cam. Each cam follower comprises
a roller 38 attached to elongate body 34 with a roller shaft 39 and further equipped
with needle bearing 40. This arrangement with rollers and needle bearings provides
a very low friction mechanism capable of damping vibration without absorbing excessive
amounts of power from the engine. Those skilled in the art will recognize in view
of this disclosure that other cam follower arrangements could be employed with the
present invention including conventional flat tappets.
[0024] Because elongate body 34 has a circular cross-section, guide plate 42 is provided
to maintain the proper alignment of the rollers with the multiple-lobed cams. The
guide plate is attached to the engine with screws 44 and assures that the elongate
body will not rotate within bearing 48.
1. A balancing mechanism for reducing the vibration of a piston type internal combustion
engine having a crankshaft (6) and a camshaft (12), said balancing mechanism comprising
one or more reciprocating balance weights (32,34) driving according to the motion
of a rotating cam (22,28), with said cam driven by either said camshaft (12) or said
crankshaft (6).
2. A balancing mechanism according to Claim 1, wherein the reciprocating balance weights
are driven by two rotating cams with at least one of said cams being driven by either
said crankshaft or said camshaft.
3. A balancing mechanism according to Claim 2, wherein at least one of said cams is
integral with either said crankshaft or said camshaft.
4. A balancing mechanism according to any one of Claims 1 to 3, wherein said balance
weight comprises an elongate body having a cam follower mounted at either end.
5. An internal combustion engine comprising a crankshaft operably associated with
one or more pistons and connecting rod assemblies having one or more multiple-lobed
cams attached thereto
a camshaft driven by, and synchronized with, said crankshaft and having one or more
intake or exhaust valves operably associated therewith, with said camshaft further
comprising one or more multiple-lobed cams attached thereto and one or more linearly
actuable balance weights mounted within said engine such that said weights are driven
reciprocably by a pair of cams comprising one of said multiple-lobed cams attached
to said crankshaft and one of said multiple-lobed cams attached to said camshaft.
6. An internal combustion engine according to Claim 5, wherein each of said multiple-lobed
cams attached to said crankshaft has two lobes and each of said multiple-lobed cams
attached to said camshaft has four lobes.
7. An internal combustion engine according to Claim 5, wherein said crankshaft has
a multiple-lobed cam attached at either end driving one of said balance weights in
conjunction with a multiple-lobed cam attached to said camshaft.
8. An internal combustion engine according to Claim 5, wherein each of said linearly
actuatable balance weights reciprocates between said pair of multiple-lobed cams.
9. An internal combustion engine according to Claim 8, wherein each of said linearly
actuatable balance weights comprises a generally elongate body having a cam follower
mounted at either end.
10. An internal combustion engine according to Claim 9, wherein each of said cam followers
comprises a roller.